1. Field of the Invention
The present invention relates to a lens actuator in an optical disc device for reading out the information recorded on the recording surface of an optical disc or recording the information, and it further relates to an optical pickup comprising the same.
2. Description of the Related Art
Since an optical disc device for recording information on a disc-like recording medium or reading out and replaying the recorded information enables recording a relatively large amount of information on the disc, and furthermore, the disc has a high stiffness and is easy to handle, it is used as an external recording device for a computer, or a video or audio recording device.
In such an optical disc device, a mechanism for driving a lens for converging or diverging a light beam from a light emitting element in the optical axis direction is a lens actuator. In general, the lens actuator comprises a movable part including a lens and a holder for holding the lens, a supporting member for supporting the movable part, and a driving part such as a motor. By applying a driving current to the driving part such as a motor, the movable part is driven. In the lens actuator, there is also a device for correcting the thickness irregularity of the transparent protective layer of an optical disc or the spherical aberration generated by traveling between the recording layers of a multiple layer recording disc. Recently, the density of optical disc has become higher and as a way to achieve it, mainly, the wavelength of the laser as light emitting element is shortened or the aperture of the object lens is enlarged. In the high density optical disc, since the above-mentioned spherical aberration deteriorates a recording or replaying signal, a device for correcting the spherical aberration is necessary. Moreover, among the high density optical discs, there are optical discs different in thickness of transparent protective layer for the same laser wavelength. For example, there are those having protective layer thicknesses of 0.6 mm and 0.1 mm and therefore, in order to correct the spherical aberration, a first lens and a second lens having different characteristics are needed.
As a lens actuator having a first lens and a second lens, there is an object lens actuator as shown in Japanese Patent Application Laid-Open No. 10-340474 (pages 3-4, FIG. 1), with the first lens and the second lens disposed side by side.
In the above-mentioned conventional technique, since the first lens and the second lens are disposed side by side, a problem is involved such that the lens actuator is bulky. Moreover, the lens has a circular ring-like portion provided on the outside of the effective diameter for the use of molding the lens. Therefore, the lens diameter is enlarged so that the lens actuator becomes further bulky, and thus it is problematic.